Image-reading devices and image-forming devices well known in the art include scanners, facsimile machines, copiers, and multifunction devices including a combination of these functions. These conventional devices use image sensors having a one-dimensional array of light-receiving elements for reading images from original documents as electronic data.
One such image-reading device disclosed in Japanese unexamined patent application publication No. 2003-298813 has a plurality of sensor IC chips arranged in a linear array and provided with a plurality of built-in photodetectors. The photodetectors receive light irradiated from a light source after the light is reflected off the original document, and the sensor IC chips are configured to output image signals of a level corresponding to the amount of received light as a serial analog signal.
The number of sensor IC chips is set to a natural multiple of three, and the sensor IC chips are divided into blocks of this natural multiple, with each block outputting an image signal. In this way, it is possible to provide an image reader capable of accelerating the process of reading an image and capable of reducing the cost of a device employed in processing image signals.
An example configuration of the image reader described above is shown in FIG. 8. Here, the sensor IC chips are divided into three blocks B1-B3, each having a corresponding cable or wiring pattern C1-C3 linking the blocks to a connector 18. The connector 18 is connected to an external circuit, such as a gate array 33, via a flexible flat cable 39. Accordingly, image signals outputted from the blocks B1-B3 of sensor IC chips are conveyed to the gate array 33 via the connector 18 and flexible flat cable 39.
With the configuration shown in FIG. 8, a reading unit 13 accommodating these sensor IC chips for reading images moves in a prescribed scanning direction, requiring that the flexible flat cable 39 have a length exceeding one meter so as not to restrict the reading unit 13 in its range of movement. Consequently, when reading and copying an image from a paper having the width of an A4-size sheet with blocks B1 and B2 of the sensor IC chips, stray capacitance, parasitic capacitance, common impedance in the ground, and other effects lead to cross talk between the adjacent wiring patterns C1 and C2. Since cross talk is the leakage of unnecessary signals, image data read by the original block B2, indicated by a solid line in FIG. 8, is leaked from the wiring pattern C2 to the wiring pattern C1 and is superposed in the copy results for the wiring pattern C1, indicated by the dotted line in FIG. 8, as if the image were read by the block B1.
In another method, the flexible flat cable 39 is covered with a shielded wire. However, this shielded wire increases the weight of the flexible flat cable 39 and is not very flexible, thereby hampering movement of the flexible flat cable 39 in the movable range of the reading unit 13. Further, such shielded wire is expensive and, therefore, increases the cost of the image-reading device.